The purpose of this contract is to conduct a study to determine the efficacy of glucosamine and glucosamine/chondroitin sulfate in knee osteoarthritis. This is a randomized, double-blind, placebo-controlled study consisting of four arms: (1) patients taking glucosamine alone, (2) patients taking chondroitin sulfate alone, (3) patients taking glucosamine and chondroitin sulfate together, and (4) patients taking a placebo. Patients will be evaluated at monthly intervals for 16 weeks and closely monitored for improvement of their osteoarthritis as well as for any possible adverse reactions to the agents. Medical evaluations and x-rays will be used to document the patients' diagnoses. The primary outcome will be measured as improvement in pain. Improvement in function will be included as a secondary outcome. An ancillary study to determine the effects of the agents on joint structure is also included as an option.